Replace Isar with SQLite for storing CLIP embeddings

[vishnukvmd]

Description

• This PR removes the dependency on Isar, and sets up a SQLite DB for storing embeddings.
• The existing DB is deleted, and the new DB is populated by pulling embeddings from the server. Local migration was possible, but that would have required us to keep Isar as a dependency for an unknown period of time.
• For 30k embeddings, DB size has dropped from ~420MB to ~115MB. The first load on a Pixel 7 has increased from ~500ms to ~600ms.
• More details @ https://ente.io/blog/tech/sqlite-objectbox-isar/#update

Tests

• Verified over internal builds that semantic search is working as expected

Note: This fixes that jank that would happen when a foreground process tries to read data from the Isar DB while a background process is alive.